Hydromechanics Labs

The experimental facilities of the Hydromechanics group comprise the laser lab and the flumes and tanks in the large experimental hall of the department.

This movie shows the movement of the particles in the silicon replica of a human aorta. The particles used in this measurement are rhodamine particles with a diameter of 200 microns. The investigation domain was illuminated by an Ar-Ion Laser.

The following movie shows the forcing device generating homogeneous isotropic turbulence to break aggregates.

This short movie shows the movement of two Barchan Dunes in our flume. The dunes consist of sand grains with d = 0.37 - 0.52 mm (top) and d = 1 mm (bottom). Pictures were taken with one of our high speed cameras (Photron SA5).

The following slide show illustrates a working day in the laser lab. It is a powerpoint presentation and takes a couple of minutes to download (21MB). The show will start automatically after download. No click is necessary to continue the presentation. Click the following link now and enjoy it!

Once upon a time in hydromechanics lab

Some results from the above experiment are shown below. The experiment is designed to clarify the blood flow in an aneurysm. Here we use a plastic model and a refractive index-matched fluid.

The model of the aneurysm.

Particle trajectories as recorded over 5 seconds, revealing a 'roll'.

Four recordings merged into a single view. Red arrows are indicating velocity. Every recording is visualized in layers of 5mm thickness, and velocity profiles are rendered in color code, if velocity is above 8cm/s.

A high-speed three-dimensional Particle Tracking Velocimetry System (3D-PTV)

Recently, the IfU purchased a unique recording system for high-speed 3D-PTV. There are two goals of this investment:

• There is an increasing interest of the Hydromechanics group in moderate and high Re_λ turbulent flows. Some recent experiments of the group, related to the stretching of Lagrangian material objects, the effect of dilute polymers and others are based on measurements at approximately Re_λ= 50. They could be repeated in higher Reynolds numbers flows. In addition, an ability to track fluid tracers that move at tens of centimeters per second will open a new field of research in the free shear and wall bounded turbulent flows.
• The major goal is to perform experiments in two-phase turbulent flows. This can be achieved by a combination of the 'old', 50Hz 3D-PTV system, shown in Fig.1 (e.g., Luethi et al. 2005, Guala et al, 2005, Liberzon et al, 2005a, 2005b) and the new, high-speed system. The combined system allows us to follow two types of particles simultaneously e.g. heavy and light particles, or heavy particles and flow tracers.

The system is based on four (4) high-speed CMOS cameras by Miktrotron (www.miktrotron.de) with 1280 x 1024 pixels, 10 bit, working at 500 fps. All four cameras are synchronized in a special way, with a maximum possible time jitter of 1/10 of the frame rate. The recording system is the only one of this type and includes the long-term streaming and storage of IO Industries (http://www.ioindustries.com), customized for our use by Cosyco (www.cosyco.de). The system includes 48 hard-disks and 4 special frame-grabbers that deliver the information directly to the array of disks.

Figure 1: 'Old' system of 4 VGA, line scanning CCD cameras of 50 Hz, 0.24 Mpixels.

Figure 2: New 3D-PTV system

Figure 3: Back and front sides of the new recording system.

Figure 4: Synchronization control, through the Streams 5 software (http://www.ioindustries.com/streams.htm)